> OK.This explains that if a process gets "migrated" from one CPU to another, the time is not "affected". But it still doesn't explain if the process gets scheduled back to the same CPU.

MPI_Wtime() doesn't tell you any of this stuff. It just tells you the time *right now*. Basically, MPI_Wtime() can be used to compute wall-clock timings (which are really the only relevant timings when measuring delivered performance, anyway).

What happens before or after that is not covered in the scope of MPI_Wtime().